1. Field of the Invention
The present invention relates to an electrical instrument, and in particular to an electrical instrument such as an AC power source having an input terminal block that allows customers to configure input power as either single phase, three phase delta, or three phase wye, without the need for an external adaptor or converter, and without modifying the internal circuitry or programming of the instrument or power source.
2. Description of Related Art
The present invention provides an improvement over the power input illustrated in FIGS. 3 and 4 of U.S. Patent Publication No. 2011/0080692, in which single phase and three phase wye and delta input connections are configured by connecting different “wiring blocks” 13 (in the form of multiple input/multiple output trace patterns shown in FIGS. 6-8) between two fixed terminal blocks T2,T3, the first of which (T1) includes three line terminals and a neutral terminal, and the second of which (T2) includes six terminals connectable to either the line or neutral terminals depending on the desired input configuration.
The power input arrangement of U.S. Publication No. 2011/0080692 has the disadvantage that, in order to change the configuration of the power input, it is necessary to replace the entire distribution circuit with another distribution circuit having a different trace pattern. This arrangement is both expensive and subject to operator error since it is possible to confuse the trace patterns and inadvertently misconnect the respective line and neutral terminals of the two fixed terminal blocks.
In contrast, instead of configuring the power input by using two fixed terminal blocks connected together by a configurable wiring blocks, a three-phase power input embodiment of the present invention utilizes a single terminal block having three line and three neutral terminals directly connectable to wires of an input power cable, with configuration being accomplished by attaching shorting bars to connect together the three line terminals or the three neutral terminals, or respective line and neutral terminals, to achieve the desired input configurations. According to the invention, there is no need to select from among multiple similarly-appearing pre-wired wiring blocks, as in U.S. Publication No. 2011/0080693, or to use an external adapter or converter. Furthermore, the invention may be adapted for additional phases by expanding the single terminal block to include additional line and neutral terminals so that the total number of line terminals and the total number of neutral terminals each equals the maximum number of input phases, and by providing appropriately dimensioned shorting bars for connecting together the line and neutral terminals according to the desired wiring configuration.
In an exemplary embodiment, the terminal block of the invention is applied to an AC power source. AC power sources are electrical instruments that convert an AC voltage and/or frequency level into another AC voltage or frequency level. For example, the AC power source may be used to convert a single phase line voltage input into a single or multiple phase electrical test voltage, to provide enhanced metering and current protection capabilities, to condition the output power to minimize power factor related losses, or to simulate voltage surges and drops during transient testing.
In typical AC power sources used for electrical testing, or to supply power for other electrical instruments, the power input is through an input terminal block having a neutral (N) screw terminal, a line (L) screw terminal, and a ground (G) connection, and is designed to accept typical line or mains voltages of between 180-284 VAC at frequencies of 47-63 Hz. Examples of AC power sources with fixed input terminal block configurations include modular AC power source model nos. 310XAC, 320XAC, and 340XAC, sold by Associated Power Technologies, Inc., of Diamond Bar, Calif. Such input power connections are simple and reliable but can only be directly connected to a single phase AC line voltage. As a result, the problem arises that when the only available external power source is a multiple phase external power source, an adapter or converter must be provided to convert the multiple phase input power into single phase input power for input through the included single phase terminal block.
The present invention provides an improvement to the single input block of the conventional power source, which allows direct connection to three phase input power supplies as well as single phase power supplies, without the need to modify the internal input circuitry or programming of the power source, without the need for an external adapter or power converter, and without the need for the multiple terminal blocks and connecting “wiring blocks” described in the above-cited U.S. Patent Publication No. 2011/0080693. While it may be used in the Associated Power Technologies™ AC power sources mentioned above, it is not limited to any particular AC power source, or even to AC power sources in general. In addition, the input terminal block of the invention may be applied to converters having a DC output, which are not strictly “AC power sources,” as well as to any power conditioner, controller, protection device or other electrical instrument having an AC input(s), including multiple function, programmable, or modular devices.
Finally, by way of general background, it has long been known to provide terminal blocks to facilitate connections between different circuits. Examples of terminals blocks in contexts other than the electrical instrument input of the present invention include the terminal block of U.S. Pat. No. 5,007,156, which is used to connect the windings of a three-phase electrical motor in either wye or delta configurations, or the terminal blocks of U.S. Pat. No. 2,785,324 and U.S. Patent Publication No. 2004/0017120, which enable switching between high and low voltage configurations by changing the interconnections between terminals of the terminal block. The present invention differs from these terminal blocks both in the specific configuration of the terminals, and in that it is applied to the particular context of providing a configurable input for an instrument, so as to enable the instrument to receive both single and multiple phase input power with different wiring configurations.